Murie et al.: Distribution and activities of Sebastes spp. 



321 



back rockfish were observed during the submersible 

 dives. The depth range and density of the relatively 

 uncommon species of rockfish may have been im- 

 proved if we had been able to do more transects and, 

 in the instance of maximum depths, by doing deeper 

 transects. Bias in using submersible transects was 

 exemplified by the downward bias (i.e. deeper) in the 

 observed minimum depth ranges for tiger, yellow- 

 tail, and yelloweye rockfish in Saanich Inlet (Table 

 2). These rockfish species have been observed dur- 

 ing SCUBA dives in Saanich Inlet in water as shal- 

 low as 15-25 m (Murie, pers. obs.). The density es- 

 timate and depth range for copper rockfish was 

 probably also biased because of the reduced ability 

 to maintain fine control of the Pisces buoyancy as 

 it approaches shallower depths (-20 m). We know 

 that copper rockfish in Saanich Inlet occur from 

 near-surface waters (~2 m) and their distribution ex- 

 tends visibly below 40 m depth (Murie, 1991). The 

 density of copper rockfish on rocky reefs in 20-30 

 m of water, however, can approach 50 fish- 100m 2 

 (Murie, 1991), far in excess of any density observed 

 for copper rockfish from the submersible (Table 2). 

 In general, however, copper rockfish do occur in 

 shallower water than quillback rockfish (Moulton, 

 1977; Richards, 1987; Murie, 1991), as was observed 

 from the submersible transects in Saanich Inlet. 



Another potentially important bias in the use of 

 the Pisces PV to observe densities and activities of 

 rockfish is whether the fish are attracted or notice- 

 ably repelled by the size, noise, and lights of the 

 submersible. Similar to our study, Carlson and 

 Straty (1981) noted that most of the rockfish were 

 neither repelled nor attracted to the submersible 

 while they observed them in southeastern Alaska. 

 In addition, Richards (1986) observed that none of 

 the common fish species seen in the northeastern 

 Strait of Georgia seemed disturbed by the Pisces PV 

 submersible. A notable exception in Carlson and 

 Straty 's (1981) study was large (7-10 kg) yelloweye 

 rockfish that were obviously attracted to the sub- 

 mersible and actually followed it, similar to the rat- 

 fish and sixgill shark in our study. Pearcy et al. 

 (1989) also noted that large schools of yellowtail 

 rockfish were attracted to their submersible and 

 followed it over substantial periods of time and 

 depth; there was no visible evidence, however, of 

 schools of yellowtail rockfish following the Pisces in 

 our study. 



The occurrence of perching and hovering activi- 

 ties observed for the majority of rockfish in Saanich 

 Inlet from the Pisces was consistent with behavioral 

 activities of quillback and copper rockfish observed 

 with SCUBA in Saanich Inlet (Murie, 1991). Obser- 

 vations from the submersible were limited in this 



respect because it was impossible to look into all 

 crevices or into shelter holes under rocks for the 

 presence of fish. Tiger and yelloweye rockfish could 

 be seen in shelter holes and crevices but their size 

 could not always be estimated. Although the Pisces 

 approaches shelter holes from below (during its as- 

 cent), fish in deep shelter holes and crevices may not 

 be detected. The presence of fish in crevices and 

 shelter holes was therefore probably underesti- 

 mated. Nevertheless, at present, submersibles and 

 remotely-operated vehicles (ROVs) provide the best 

 means of observing the activities of rockfish occu- 

 pying complex habitat in deep water. 



Although it is evident from submersible observa- 

 tions that estimates of abundance and activities of 

 rockfish involve a variety of biases, these direct vi- 

 sual assessments can provide quantitative informa- 

 tion on the densities and depth distributions of rock- 

 fish species in habitats that cannot be surveyed ad- 

 equately using bottom trawls. In addition, 

 submersibles allow direct observation of the behav- 

 ioral activities and associations of individual fish in 

 relation to specific habitat types. This type of infor- 

 mation has not been attainable using conventional 

 survey techniques of fisheries. 



Acknowledgments 



We are especially grateful to T Fitch and the pilots 

 and crew of the Pisces PV (Institute of Ocean Sci- 

 ences, Department of Fisheries and Oceans, Sidney, 

 B.C. ) who provided the opportunity and expertise to 

 work efficiently with the submersible. We thank Q. 

 Liu for analyzing the hydrocast samples, and J. 

 Gilbert and C. Steinhoff for rockfish observations. 

 Constructive comments by F. Matthews, L. 

 Richards, J. Mclnerney, N. Wilimovsky, R Gregory, 

 V. Tunnicliffe, D. Mitchell, C. Tolman, and two 

 anonymous reviewers improved the manuscript. 

 Financial support was provided by a Postgraduate 

 Scholarship from the Natural Sciences and Engi- 

 neering Research Council of Canada (DJM) and by 

 the Biology Department, University of Victoria. 



Literature cited 



Anderson, J. J., and A. H. Devol. 



1973. Deep water renewal in Saanich Inlet, an in- 

 termittently anoxic basin. Estuarine and Coastal 

 Mar. Sci. 1:1-10. 



